The present invention relates to a process for forming a permalloy film pattern serving as a magnetic layer of a thin film magnetic head, and particularly to a chemical etching process for forming the side edges of a permalloy film pattern in a tapered state.
In FIG. 1, a structure of a magnetoresistive head, a kind of thin film magnetic head, is shown, where a magnetoresistive head is formed by laminating a lower magnetic layer (permalloy film) 2, a magnetoresistive film 3, a conductor 4 and an upper magnetic layer (permalloy film) 5 one upon another on a ceramic substrate 1 according to a film-forming technique such as a resistance-heating, vapor deposition procedure, etc. Insulating layers 6 and 7 are provided between the lower magnetic layer and the magnetoresistive film 3 and between the magnetoresistive film 3 and the upper magnetic layer 5 to form gaps therebetween.
Suitable material for the lower and upper magnetic layer is a Fe-Ni based alloy (permalloy) having a high saturation magnetic flux density and a high initial permeability.
To prevent a magnetic saturation in a magnetic layer and enable read-out of information recorded at a high density, it is necessary that the permalloy film usually has a thickness of at least 1 .mu.m. In forming patterns of such a relatively thick film by photoetching for use as a magnetic layer, the film thickness at the side edges of a pattern must be gradually reduced in a tapered state, because, as shown in FIG. 2, when an insulating layer 6 or a conductor film 4 as constituents for a thin film magnetic head is laminated onto a magnetic layer pattern 2 having sharply inclined side edges, formed on a substrate 1, the film thickness is usually considerably thinner at a side edge 8, with ready occurrences of peeling of laminated film, or insulation failure or conductance failure.
To obtain a permalloy film pattern having tapered side edges, it has been so far proposed (1) to provide an auxiliary layer consisting of at least one of titanium, titanium oxide, and silicon oxide between the permalloy film and a photoresist film, and etch the layer in an etching solution containing hydrogen fluoride at the same time, (2) to provide an auxiliary layer consisting of a permalloy film having a higher iron content than that of the base permalloy film therebetween, and etch the layer, and (3) to provide an auxiliary layer consisting of a permalloy film formed at a lower substrate temperature than that of the base permalloy film therebetween and etch the layer. These procedures are to obtain tapered side edges by utilizing the fact that the etching rate of the auxiliary layer is higher than that of the base permalloy film. However, the said procedure (1) has a serious practical disadvantage that no permalloy film is formed on a substrate containing SiO.sub.2 as the major component, because the substrate surface is corroded by hydrogen fluoride during the etching. The said procedures (2) and (3) also have such disadvantages as not only deterioration of magnetic properties of permalloy film, but also less reproducibility.